This invention relates generally to heat exchangers for air conditioning systems and, more particularly, to a method and apparatus for leak testing of heat exchangers to be charged with refrigerant.
In the manufacture of air conditioning systems of the type installed for residential use, for example, a heat exchanger coil is used in both the indoor and outdoor units. When installed, the refrigeration circuit is charged with refrigerant, and it is important that this charge be maintained for prolonged periods of time. That is, any significant leakages that may occur will cause inefficient and ineffective operation, thereby requiring a service call for recharging and possibly repair of a leaky coil.
Because of the number of tubes involved, and the significant number of steps involved in the process of fabricating a heat exchanger, the most likely place for a leak to occur in an air conditioning system, is in a heat exchanger. Accordingly, it is important, for quality control purposes, that a relatively high percentage of heat exchangers coming off the production line be leak tested.
One known method of leak testing of heat exchangers is to pressurize the heat exchanger with a trace gas which, if there are any significant leaks in the heat exchanger, can be detected and located with the use of an appropriate sensing device. This process is usually applied to the individual heat exchangers prior to their being incorporated into the system so that any leaks can be corrected relatively easily. However, in the case of room air conditioners, for example, it may be desirable to wait until the system is assembled such that the unit may be charged as a unit, tested, and then shipped in the charged condition.
One type of trace gas that may be used for leak testing is the refrigerant itself, particularly where the system is precharged and tested as described hereinabove. Another common approach is to use a stable inert gas, such as helium, in combination with a helium detector. In order to reduce costs and facilitate the flushing process, the helium gas may be diluted with another inert gas, such as nitrogen or air, while still being detectable by the detection device.
Another type of gas that is becoming more commonly used is hexafluosulfide (SF6). While this gas is more stable and also more sensitive to the detectors such that less gas is needed during the testing process, any leakage to the atmosphere is a greater problem for global warming because its stability prevents it from breaking down.
With any of the above approaches, the leakage of the trace gas can be a problem in two respects. First, any leakage of the gas into the atmosphere is environmentally undesirable, particularly with higher standards being required in the marketplace. Secondly, the loss of the trace gas becomes a cost factor if it is wasted and not re-used.
It is therefore an object of the present invention to provide an improved method and apparatus for leak testing of heat exchanger coils.
Another object of the present invention is the provision for a leak testing method which reduces the occurrence of introducing trace gases to the environment.
Yet another object of the present invention is the provision for reducing the waste that results from loss of trace gases during leak testing.
Still another object of the present invention is the provision for a heat exchanger leak testing process that is efficient and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.
Briefly, in accordance with one aspect of the invention, an outer leak free container is provided around an inner leak free container, with the inner container having the trace gas sensing system disposed therein. A heat exchanger to be tested is installed in the inner container, which is then closed. A vacuum is drawn on the space between the two containers. The heat exchanger is pressurized with a trace gas and the detector is activated to sense and locate any inner leak in the heat exchanger. Any trace gas leakage is contained within the two containers.
By another aspect of the invention, the inner container is fluidly connected to a recovery system, which in turn is fluidly connected to the charging system, such that any leaked trace gas can be returned to the system.
In accordance with another aspect of the invention, one or more extractors are provided to cause any leaked trace gas to pass from the internal container to the recovery system.
In accordance with yet another aspect of the invention, the outer container under vacuum serves as a backup container from an escape of gas from the inner container to guarantee a zero emission testing system and thus make the system environmentally friendly.
In the drawings as hereinafter described, a preferred embodiment is depicted; however various other modifications and alternate constructions can be made thereto without departing from the true spirt and scope of the invention.